"The Coolgardie Safe was made of wire mesh, hessian, a wooden frame and had a galvanised iron tray on top. The galvanised iron tray was filled with water. The hessian bag was hung over the side with one of the ends in the tray to soak up the water.

Gradually the hessian bag would get wet. When a breeze came it would go through the wet bag and evaporate the water. This would cool the air and in turn cool the food stored in the safe.

It was usually placed on a veranda where there was a breeze. The Coolgardie safe was a common household item in Australia up to the mid-twentieth century. Safes could be purchased ready-made or fairly easily constructed at home. Some of the metal panel safes are very highly decorated, showing the great creativity of their makers."

Source Wikipedia

I would like to know how much cooler it makes the food. Does it drop the temperature more than 20 degrees?

It is a very popular thing here in Andalucia.

Don't want to take even a tiny bit away from this man, but the same fundamental principle is involved it at least a few things that have been around a while. The ones that come to mind:

Look at movies of the Okies migrating--all those cars had one or more water bags, made from canvass, that kept the water cool by evaporating a little of the water.

You might also see in the windows of some of the cars, and on roofs and in windows of some homes things some of us called "swamp coolers" or just "coolers" where water flowed across a fiber mat (I don't remember what the mat was made of--sisal? hemp? while air flowed through the mat into the car or house.

In hot weather I wear cotton flannel shirts (over the cotton T-shirts I wear year-round) so the sweat will evoporate and cool me a bit.

I suspect the cloth down the back of the neck might do the same thing.

Where I lived as a little kid, houses didn't have basements or cellars usually, but they often had "coolers" which were cupboards with hardwae cloth for shelves, and open to the crawl space (damp earth--cool) and the attic). Most of the food we now keep in the refrigerator would have been keep in the cooler because ice for the ice box was expensive.

Perfect for the next hurricane here.
THNX Gail.